There's also no evidence of a regular mass extinction cycle as the OP states. If anything, the evidence indicates that mass extinction events are becoming LESS frequent over time. For example, there was no mass extinction event between the Triassic-Jurassic and the end-Cretaceous events. That's a period of nearly 150 million years, and well outside the "27 million year cycle."
Does that mean there's NOT something beyond Pluto? Of course not! However it also shows that one of the pieces of proposed evidence is invalid.